Study: Expect slower, more devastating hurricanes

Imagine more hurricanes like Florence — or even more powerful — that hover over coastal communities longer, allowing them to dump ever-record-setting deluges that devastate lives and property.

A recent study in the journal Nature suggests more such outcomes due to hurricanes slowing down. It's already happening, researchers say: Hurricanes have slowed by about 10 percent between 1949 and 2016, the researchers found, bringing longer suffering to those in their paths. 

"All of the bad things that come with a hurricane get worse," said Jim Kossin, the paper’s author and a scientist with the National Oceanic and Atmospheric Administration, or NOAA. "You get the winds acting on things longer. You get increased storm surge."

But the most direct impact will be Hurricane-Harvey-like rains — overall, a 10 percent increase in rains over a given area.

"Just like Harvey, if you stall a storm, you get a lot of rain in one place," Kossin said.

Hurricane Harvey slammed Houston, Texas, last year, dumping more than 40 inches of rain in some areas.

Researchers aren't sure whether the hurricane slowdown is driven by climate change or is simply a natural variation.

Not only are hurricanes slowing, but globally, they seem to be changing where they're going.

In a separate study, also published in Nature in 2014, Kosslin and his colleagues found a trend of tropical cyclones moving poleward in the global historical data in both the Northern and the Southern hemispheres, with rates of 53 and 62 kilometers per decade, respectively.

The greatest migration is found in the northern and southern Pacific and South Indian oceans, the researchers found, but there is no evidence yet that the peak intensity of Atlantic hurricanes has migrated poleward in the past 30 years. That poleward trend isn't expected to take shape in the Atlantic Ocean for several decades, Kosslin said.

"The Atlantic is sort of beating to its own drummer," he said. "You could potentially talk about what's going to happen in the next 50 years from now ... It's hard to say if and when we're going to see these things migrating poleward (in the Atlantic)."

As tropical cyclones elsewhere move into higher latitudes, some regions closer to the equator may see reduced risk, the researchers say, while coastal populations and infrastructure poleward of the tropics may experience increased risk, especially for coastal cities not accustomed to hurricanes. Also, regions in the tropics that depend on rains from tropical cyclones to help replenish water resources may be at increased risk for lower water supply as the storms migrate away from them.

The researchers looked at locations where tropical cyclones reach their maximum intensity.

Scientists have linked the expansion of the tropics in part to human-caused increases of greenhouse gases, stratospheric ozone depletion and increases in atmospheric pollution. 

But determining whether the poleward shift of tropical cyclone maximum strength can be linked to human activity will require more and longer-term investigations, they said.

The same uncertainty holds true of slowing hurricanes, Kosslin said.

"We're not really sure yet exactly what is causing that," he said. "But it's at least consistent with what we might expect as the planet warms."

Contact Waymer at 321-242-3663 or jwaymer@floridatoday.com.

Twitter: @JWayEnviro

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